The goal of this proposal is to develop a novel detector/imaging device for positron emission imaging. A basic detector module will consist of an LSO crystal cut into parallet-piped elements and coupled to a matched Silicon Drift Photodetector (SDP) array whose elements provide excellent energy and timing resolution. The proposed system is intended to eliminate the need for photomultiplier tubes and allow for intergration of electronics with the detector leading to lower cost PET systems. We plan to develop an imaging system utilizing a pair of 4 inch diameter LSO/SDP modules, each consisting of 40 x 40 detector pixels, optimized for use with FDG for detection of breast cancer. A coincidence imaging device optimized for breast imaging has the potential of improving on the sensitivity (x20), count rate and spatial resolution versus a full PET system. The development of the 2-detector module breast imager will allow basic detector development to occur along with the development of a needed product to improve cancer detection. Improved sensitivity will result in better image quality, reduced imaging time or smaller injected doses. The proposed detector development program has specific goals divided into two technical phases. Phase 1: Design optimized detector structure leading to the targeted performance for electronic noise, quantum efficiency, narrow transit time of electrons; (2) Fabricate prototype 8 x 8 SDP array; (3) Evaluate parameters of the devise to measure the potential for success for long term aims of the project. Phase 2: (1) Develop final SDP array structures with integrated input transistor-preamplifier; (2) Develop housing, specialized processing and display electronics and reconstruction software; and (3) Construct and evaluate prototype detector system under simulated clinical conditions before deployment for testing at the UCLA Iris Cantor Breast Center. PROPOSED COMMERCIAL APPLICATION In the third phase we will commercialize single and multiple detector modules based upon the Phase 1 and Phase 2 efforts, as well as a complete dedicated system for clinical use in positron emission imaging for detection of breast cancer. These new detectors will lead to lower cost PET detector systems by utilizing a new SDP which needs only low cost silicon planar processing and allows integration of electronics with the detector. There are large needs and potential for commercial uses for such PMT replacements for PET.